Next on CSI: Using Saliva to Tell a Person’s Age

If you’re a fan of CSI, you know that dead men don’t tell lies. Not even about their age.

But it wasn’t until a new discovery by researchers at the University of California, Los Angeles, that scientists could actually determine a person’s age using genetic material. Despite the sophistication of the latest tools of forensic science, it hasn’t been possible to establish definitively the age of a specific tissue sample or cell. DNA, it seems, doesn’t give away your age.

But on Wednesday, UCLA researchers reported in the journal Public Library of Science ONE (PLoS ONE) that for the first time, they may be able to glean age from genetic material. Working with saliva samples, the team focused on epigenetic changes to DNA. These alterations — which are caused by environmental influences like diet, stress, exposure to sunlight and carcinogens and even toxins — do not change the DNA itself, but are layered on top of the genome, affecting how genes are turned on or off. At specific areas of the genome, say the scientists, these changes build up or decrease in almost chronological fashion, allowing them to serve as a timeline to predict a person’s age to within five years.

“It’s a really new way of looking at genes in a totally non-static way, in a dynamic way that is highly dependent on the environment,” says Eric Vilain, lead author of the study and director of the Center for Society and Genetics at UCLA.

Vilain didn’t actually start out looking for a way to chronologically age DNA. As a genetic researcher with an interest in sexual orientation, he was studying twins who were discordant in sexual identity — one sibling being gay, while the other was straight — to see if there were any environmentally caused epigenetic changes to gene expression that might be contributing to the difference.

In trying to find a potential nurture explanation in the nature-nurture debate over sexual orientation, he instead stumbled across the interesting finding association epigenetic changes and age. “Almost right away we found a very, very strong effect of age between the twin pairs,” says Vilain.

The older the twins, the more likely they were to have epigenetic changes, measured by the attachment of a carbon-based methyl group on to their genes. “We had some twins who were 20 years old, and others who were 50 and others who were 75. When we measured the chemical modification of their DNA, we found it was highly correlated with age,” he says.

The UCLA team validated their findings by turning to a random group of non-twin participants and analyzing their DNA’s epigenetic changes the same way. Sure enough, says Vilian, the team was able to predict the participants’ age to within five years based on changes at only two the sites on the epigenome.

He stresses that the findings do not suggest that aging can be reduced down to the activity of these epigenetic changes; rather, they seem to be indicative of a pretty complete set of the methylation changes that occur as a person ages. Not surprisingly, the two sites are involved in things like risk of Parkinson’s disease, which is strongly age-dependent, and loss of hair, teeth and lowered immune function, again factors we link to aging.

On the forensic side, the link between epigenetic changes and age will needs to be replicated and confirmed by other groups before you’ll see it being used in real crime scene investigations. Going forward, Vilain is eager to find out if the process works as well on other types of tissue such as hair, skin, blood and sperm.

It’s also not clear how robustly these epigenetic changes can be maintained in these tissues. For example, would they still be observable in a body that had drowned or been buried or exposed to the elements?

Forensics would be only the first area of applications of this epigenetic bonanza. Vilain also envisions studying aging outliers who seem to have “younger” epigenomes compared with their chronological age, to determine if they possess some biological advantage to longevity. That might lead to treatments or interventions for the outliers on the other end — those whose cells seem older than their chronological age. “Maybe we can slow down bio-aging,” he says. “That would be quite an exciting concept.”